As the cost of petrol based chemicals continues to rise, more economical ways to effectively reclaim scrapped materials are needed. In the case of biaxially oriented crystallizable thermoplastics films, the recycling of clean film is straight forward and well known. Difficulties arise when the films have been subsequently processed, having been coated, dyed, printed, laminated, or the like. Coatings may be applied in-line during the manufacturing of the film or may be applied off-line by any number of methods including solvent based, aqueous based, or extrusion coated. Many of these coatings are not miscible in the base polymer used in the original film making, rendering recycled film containing such coatings unsuitable for recycling into new biaxially oriented film. Immiscible coatings tend to agglomerate and cause both process and quality issues in the new film. Filters are typically used in the extrusion portion of the film manufacturing process to remove normal levels of contaminants from the coatings. These filters can also remove agglomerated coatings, however, when an appropriate mesh size is used to filter the agglomerates, the filters tend to clog rapidly thereby reducing the effective filter life and increasing production costs. Further, agglomerated coatings that pass through the filter can cause process instability during the orientation portion of the film manufacturing process and can also leave gels that appear as optical defects in the finished film.
Some biaxially oriented films made from recycled, coated, crystallizable, thermoplastics, in particular from crystallizable polyesters, are known.
For example, U.S. Publication No. 2011/0168325A1 describes a process for recycling coated waste film from a release liner application. However, there is no mention of compatibility issues with the residual coating. Further, the process is focused on increasing the IV and also describes the necessity of adding a coloring agent to mask yellowness associated with the recycling process.
U.S. Pat. No. 6,436,322 describes a process for recycling polyester terephthalate (PET) flakes characterized by extrusion under vacuum while homogenously injecting an inert gas, or steam, to strip the PET granulate of volatile contaminants. This process also calls for a subsequent step of solids re-condensation in the solid state in order to raise the IV to sufficient level for reuse in PET bottle making.
U.S. Publication No. 2007/0161719A1 describes a method of recycling immiscible and/or cross-linked scrap polymeric material using shear mastication by combining said material with an uncross-linked, lower molecular weight polymer. Following the high shear mastication portion of the recycling process, the described method relies on adding a lower molecular weight polymeric material to the recycled polymeric material at a critical point so as to prevent cross-linked particles from reforming molecular bonds